1. Technical Field
The present invention relates generally to methods and devices for the measurement of the color of reflected and emitted light, and particularly to a handheld calorimeter.
2. Description of Related Art
Many fields of endeavor require quick accurate measure of the color of objects, or a comparison between objects. In addition, there are many color blind people that have difficulty accurately judging colors to varying degrees. There are also people who may not be color blind, but have simply not learned all of the subtle color variations and names. When these people read books, work on a computer, shop for clothes, etc., they may not always be able to tell the color of the objects at which they are looking.
Currently, handheld calorimeters are available for measuring the color of an object. These devices measure color by placing the tip of the probe against (or in close proximity to) the surface of the object being measured. The calorimeter generates a single measurement from three data points representing the reflectance of the three primary colors red, green, and blue (RGB). The single color value can then be compared to a preloaded table of color values.
However, current handheld calorimeters have several limitations. Current calorimeters cannot measure color at a distance and have problems handling ambient light. Current methods also have problems with changes in the intensity of artificial lights, such as florescent lights. In addition, the prior art requires recalibration by the user upon every use.
Therefore, it would be desirable to have a handheld calorimeter that can measure the color of distant objects and can properly compensate for ambient light, without the need for constant recalibration.
The present invention provides a handheld, pen-like colorimeter for measuring the color of an object. The colorimeter comprises several light emitters, each with distinct color spectra, wherein the emission of each color is modulated at a specific frequency. These light emitters may be Light Emitting Diodes (LEDs) and/or lasers. The colorimeter also contains at least one light sensor which samples light reflected from an object illuminated by the light emitters. The rate of sampling is at least twice the modulation frequency of the emitted light. A microprocessor computes the fourier transform of the intensity of the reflected light over time, wherein the fourier transform provides the light intensity at each possible modulation frequency and determines the relative contribution of the reflected light from each light emitter, as well as the contribution of ambient light. The modulation frequency of the light emitters is adjusted to account for the modulation frequency of artificial, ambient light. A color value based on the fourier transform of the reflected light is calculated and then mapped to a list of color values from which a color name is selected and presented to the user.